1. Field of the Disclosure
The present disclosure relates to a noise reduction method for reducing noise such as road noise inside a vehicle, and particularly to noise reduction control depending on a driving situation such as automatic driving or manual driving.
2. Description of the Related Art
When a person listens to music via CD, DVD or radio broadcasting in a vehicle, he/she is exposed to noise such as engine noise or road noise and cannot listen to music well. In order to address the situation, a noise cancel system for removing or reducing noise is provided in the vehicle. With the noise cancel system, a microphone is installed inside a vehicle, noise is extracted from external sound via the microphone, and a noise cancel signal for canceling noise from the extracted noise is generated and is output together with an audio signal.
JP 2006-213297 A discloses an active noise vibration control apparatus for preventing a reduction in vibration in a specific frequency band. JP 2006-213297 A describes a method for preventing a reduction in sound which may be comfortable for the passengers, such as engine sound or exhaust sound.
Advanced image processing techniques, communication techniques, high-accuracy vehicle location calculation techniques, and the like are enhanced and are being studied and developed for practical use in automatic driving. Further, to control automatic diving at some levels is being discussed depending on factors such as vehicle-mounted functions, road types, or traveling environments. According to the control, complete automatic driving is performed in one zone during traveling, while semi-automatic driving or manual driving is performed in another zone.
When the driving is switched to complete automatic driving, semi-automatic driving, or manual driving, it is desired to realize a noise reduction function depending on the driving situation. For example, it is desired to strongly apply the noise cancel function to provide a quiet space inside the vehicle during complete automatic driving, while it is desired to weakly apply the noise cancel function to enable the driver to listen to external sound such as engine sound or exhaust sound during manual driving.